Rear brake options??

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don4life

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Jun 22, 2014
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My 85 T-type has had the 8.5 rear removed and replaced with a Monty SS 7.5 rear but for some reason they kept all the rear brake hardware including backing plates and all. So I need a decently priced rear brake setup that is preferably a disc brake for a Gm 7.5 rear, just dont want to spend money putting factory brakes on it if Im going to replace with something better. Also plan on looking for a 8.5 posi rear in a few month to put back into my car. Also my car is a factory Hydro boost and im not sure it that effects adding rear disc brakes or not?
 

clean8485

Comic Book Super Hero
Dec 18, 2005
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The A/G body rear axle assemblies use the same drum brake setup, whether its 7.5 or 8.5, so there's no difference there. The backing plates, shoes, drums, wheel cylinders, etc are the same between both axles.
As Anubis has said, the Camaro rear disc setup is probably your best bet, just be careful to make sure that the rims will clear the disc brakes.
The factory Buick hydroboost has been known to have issues with reliability. If you could istall a vacuum power brake assist on the car, you'll probably be better off. Good luck.
 

ssbrewskyaz

Master Mechanic
Dec 29, 2010
472
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New River, Arizona
For what it's worth, the 98-02 Z28 (LS1) rear brakes really would work the best and have an excellent park brake set up with an internal hat rotor. Unfortunately, this arrangement is not without its issues. The main issue is the caliper is designed to be mounted inboard or towards the middle of the car (better balance). This presents a clearance issue with the G-Body frame during suspension compression. That is unless you mount the calipers outboard, towards the rear of the car. In order to do this, you'll need to mount the calipers upside down on the opposite sides they were designed for or essentially hanging off the rear of the car. When faced toward the rear of the car, there is no frame clearance issue.

You could also use 93-97 Z28 rear brakes. These calipers have an internal park brake mechanism and do not use the rotor with the internal hat and shoe type eBrake. Also, they were designed originally to be mounted outboard, toward the rear of the car, so again, no frame clearance issue. This set up is similar to the majority of rear disc brake swaps that typically use a Cadillac rear caliper with an internal park brake function. Effective but not nearly as clean as the internal hat rotor park brake.

I really prefer the 98-02 setup but am absolutely less than thrilled about installing parts upside down and on opposite sides they were designed for. Unfortunately, the only other alternative I can see at this point would be to relieve the frame in the contact area, or essentially, major on car surgery. Just sayin. ...








:arrow: :roll: :arrow: :? :arrow: :shock: :arrow:...Scott...
 

clean8485

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Dec 18, 2005
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I have a couple of questions.
First off, I understand that 4 wheel disc brakes provide better stopping power, and that they also can look pretty trick, especially on a vehicle that didn't originally come with them from the factory. The first question that I have is, how much more stopping power do they provide, as compared to the factory disc/drum setup that's in good condition? I've seen and read about improvements that can be done to the factory rear drum brakes, including using all primary brake shoes, and wheel cylinders with larger bore pistons (S10 wheel cylinders). With the possible problems that can arise with trying to retrofit disc brakes on the rear of these cars (caliper interferance, park brake type and installation), how advantageous is it to convert to disc brakes on the rear? Is it really worthwhile?
Now I know that this question has probably been asked before, but secondly, is there any kind of writeup that shows a complete overview of a 4 wheel disc brake conversion on these cars, including the compatibility of the original hydraulic system (stock master cylinder, stock proportioning valve), with a 4 wheel disc brake setup?
The way I see it, you can overcome the mechanical issues (caliper fitment, park brake, wheel clearance) of a 4 wheel disc brake conversion, but you still need a hydraulic system, that's going to operate the front and rear brakes with the proper balance, and without causing brake lockup issues.
Just sayin'.
 

ssn696

Living in the Past
Supporting Member
Jul 19, 2009
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Nice step-by-step here: http://gbodyforum.com/viewtopic.php?f=1 ... DFjFRZAHhQ

Does not go into the changes up front. I think you can use the factory master cylinder, but need to change the proportioning valve, check out Inline Tube. The best would be to add an adjustable valve inline to dial-in the rears to just below lockup at max pedal effort.
 

ssbrewskyaz

Master Mechanic
Dec 29, 2010
472
102
43
New River, Arizona
Jeff,

In my opinion, your point is valid. A person can make rear drum brakes perform to a satisfactory level and especially for what most on this site will be doing with their cars. To do that however requires a routine of adjustment.

I think almost everyone agrees on the reason to swap out front drums for discs. Some of the same logic applies to the rears as well. With front drums, depending on the weather, a person never knew which way the car would pull when the brakes were applied. Throw in rain or water and the issue is compounded. Some of that still applies to rear drums. Unless both left and right are adjusted equally, one sides friction material (shoe) will engage the drum before the other causing who knows what on hard braking.

Disc brakes provide significant cooling improvements over the drums. In rear drum brakes the heat is mostly retained in the drum so brake fade occurs faster and takes longer to dissipate. This was the reason for the aluminum brake drums on some of the GM cars. Still not a perfect scenario but much better heat rejection than steel.

Two things for me, rear drum brakes, especially on trucks, eventually are typically just along for the ride. While they do provide some stopping assist, they're typically out of adjustment and do not afford the user the full capacity of the available brake resources. This is primarily because of the way the adjusters are designed. In theory, the adjusters should adjust the rear shoes up incrementally each time a person backs up. Unfortunately, due to the crud and corrosion that occurs over time, a person literally has to jam on the brakes in reverse to accommodate the adjustment. People just don't drive like that and hence the rear shoes tend not to self adjust. The result is as previously stated, they're just along for the ride.

Other than that, rear discs look way cooler, stop better on average, require no adjustment, make less dust, brake pad wear can be determined with minimal effort and so on.

Now, with all that said, there's gonna be somebody that wants to argue about how great their rear drums are. Good for them, not my deal.

Scott, ...


:arrow: 8) :arrow: :wink: :arrow: :) :arrow:
 

pontiacgp

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Mar 31, 2006
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For street use drum brakes in the rear are good. There is still transport trucks on the road that have drum brakes up front. The problem that arises with drum brakes is under conditions where the brakes are used very hard and frequently is the drums expand and you loose pedal since the rear brakes give you your pedal height. I havn't converted my rear brakes yet (I'm lazy) but I can say with the A body rear that has the cylinder bolted in place the rear brakes work alot better than the G body brakes with the clip.
 
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